Quality factor for localized defect modes in a photonic crystal slab upon a low-index dielectric substrate

Localized defect modes in a two-dimensional photonic crystal slab upon a SiO(2) substrate have been analyzed by a numerical simulation of dipole radiation based on the finite-difference time-domain method. A degenerate pair of the defect mode of E(1) spatial symmetry was found in a pseudogap in the spectrum of dipole radiation. We achieved a quality factor as large as 800 by optimizing the sample geometry.